Experimental Investigation of Influence of Dissolved Salts and Surfactant on Heat Transfer in Atomized Spray Quenching of Metal

2010 ◽  
Author(s):  
Umair Alam ◽  
Khalid Abd alrahman ◽  
Eckehard Specht
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Temperature Measurement ◽  
Pure Water ◽  
The Other ◽  
Film Boiling ◽  
Wetting Front ◽  
Maximum Heat ◽  
Boiling Regime ◽  
Front Position

Spray quenching is widely used in industrial applications. In atomized spray quenching (ASQ), water and air are supplied to the nozzle at a certain flow rate and pressure to produce a full cone spray consisting of discrete droplets. Impingement density of spray i.e. coolant mass flow per unit area per second is considered to be the most influential parameter for heat transfer. Impingement density varies with radius and so as the heat flux. Water quality is altered by adding five different salts i.e. NaCl, Na2SO4, NaHCO3, Na2CO3, and MgSO4 in de-ionized water with various concentrations. On the other hand, a surfactant Ethoxylated ester, which is commonly added in cooling water in cast houses of metals, is added to pure water in different concentrations i.e 50, 100, 200 and 500ppm. A circular disc made of Nickel of thickness 2mm is heated to 600°C and sprayed on one side by atomized spray and the temperature distribution with respect to time is measured using Infrared camera on the other side of the disc. By this IR thermography, transient temperature measurement can be done within the window of 320×80 pixels with a minimum pixel real distance of 1mm on the sheet surface. Frequency of measurement is 150Hz. Since the temperature measurement and cooling sides are opposite at 2mm thickness apart, inverse heat conduction problem is solved by applying finite element method for calculating temperature and heat flux on the quenched side of metal sheet with respect to space and time. It has been observed that increasing the concentration of salts increase the leidenfrost point and shortens the film boiling regime. While addition of surfactants decrease the leidenfrost point and prolong the film boiling regime. Maximum heat flux position is considered as the wetting front position. There is an abrupt variation of heat flux at wetting front position due to the change of boiling phenomenon. Wetting front velocity has been compared for salt solutions, surfactant and de-ionized or pure water.

A Photographic Study on the Effects of Hydrophobic-Spot Size and Subcooling on Local Film Boiling

2013 ◽  
Author(s):  
Bambang Joko Suroto ◽  
Masahiro Tashiro ◽  
Sana Hirabayashi ◽  
Sumitomo Hidaka ◽  
Masamichi Kohno ◽  
...  
Keyword(s):  
Heat Flux ◽  
High Speed ◽  
Bubble Dynamics ◽  
Pure Water ◽  
Nucleate Boiling ◽  
Spot Size ◽  
Copper Surface ◽  
Film Boiling ◽  
Working Fluid ◽  
Boiling Regime

The effects of hydrophobic circle spot size and subcooling on local film boiling phenomenon from the copper surface with single PTFE (Polytetrafluoroethylene) hydrophobic circle spot at low heat flux has been investigated. The experiments were performed using pure water as the working fluid and subcooling ranging from 0 and 10K. The heat transfer surfaces are used polished copper block with single PTFE hydrophobic circle spot of diameters 2, 4 and 6 mm, respectively. A high-speed camera was used to capture bubble dynamics and disclosed the sequence of the process leading to local film boiling. The result shows that local films boiling occurs on the PTFE circle spot at low heat flux and was triggered by the merging of neighboring bubbles. The study also showed that transition time required for change from nucleate boiling regime to local film boiling regime depends on the diameter of the hydrophobic circle spot and the subcooling. A stable local film boiling occurs at the smallest diameter of hydrophobic spot. Subcooling cause the local film boiling occur at negative superheat and oscillation of bubble dome.

scholarly journals ELETRIC FIELD ENHANCEMENT AND DETERIORATION OF BOILING HEAT TRANSFER AND CRITICAL HEAT FLUX IN DIELECTRIC FLUIDS

2001 ◽  
Vol 1 (1) ◽  
pp. 32
Author(s):  
P. M. Carrica ◽  
V. Masson
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Electric Fields ◽  
Boiling Heat Transfer ◽  
Nucleate Boiling ◽  
Film Boiling ◽  
Two Phase ◽  
Boiling Regime ◽  
Dielectric Fluids

We present the results of an experimental study of the effects of externally imposed electric fields on boiling heat transfer and critical heat flux (CHF) in dielectric fluids. The study comprises the analysis of geometries that, under the effects of electric fields, cause the bubbles either to be pushed toward the heater or away from it. A local phase detection probe was used to measure the void fraction and the interfacial impact rate near the heater. It was found that the critical heat flux can be either augmented or reduced with the application of an electric field, depending on the direction of . In addition, the heat transfer can be slightly enhanced or degraded depending on the heat flux. The study of the two-phase flow in nucleate boiling, only for the case of favorable dielectrophoretic forces, reveals that the application of an electric field reduces the bubble detection time and increases the detachment frequency. It also shows that the two-phase flow characteristics of the second film boiling regime resemble more a nucleate boiling regime than a film boiling regime.

Flow Film Boiling From a Sphere to Subcooled Freon-11

1986 ◽  
Vol 108 (4) ◽  
pp. 934-938 ◽  
Author(s):  
J. A. Orozco ◽  
L. C. Witte
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Liquid Velocity ◽  
Flow Boiling ◽  
Empirical Correlation ◽  
The Other ◽  
Film Boiling ◽  
Vapor Film ◽  
Peak Heat Flux ◽  
Semi Empirical

The boiling curves for flow boiling of freon-11 from a fluid-heated 3.81-cm-dia copper sphere showed dual maxima. One maximum corresponded to the nucleate peak heat flux while the other was caused by transitory behavior of the wake behind the sphere. Film boiling data were predicted well by the theory of Witte and Orozco. A semi-empirical correlation of the film boiling data accounting for both liquid velocity and subcooling predicted the heat transfer to within +/− 20 percent. The conditions at which the vapor film became unstable were also determined for various sub-coolings and velocities.

Wetting Front Tracking During Metal Quenching Using Array of Jets

2010 ◽  
Author(s):  
Khalid H. M. Abdalrahman ◽  
Umair Alam ◽  
Eckehard Specht
Keyword(s):  
Heat Flux ◽  
Nucleate Boiling ◽  
Temperature Data ◽  
Film Boiling ◽  
Wetting Front ◽  
Inverse Algorithm ◽  
Maximum Heat ◽  
Water Jets ◽  
Maximum Heat Flux ◽  
Hot Surface

Metal quenching is a commonly used heat treatment technique, e.g. Direct Chill aluminum casting, quenching of steel for obtaining desired micro-structures. Film boiling, transition boiling, nucleate boiling and forced convection are the mechanisms of heat transfer during quenching. When the coolant strikes the hot metal surface during quenching, the surface can be divided into two distinct zones which are dry and wet zones. Heat transfer in dry zone is dominated by film boiling and the wet zone is influenced by transition boiling, nucleate boiling and forced convection. Wetting front is the boundary zone which separates the dry and wet regions. Wetting front is a thin region of coolant in which the transition and nucleate boiling occurs. Within a wetting front, the heat flux leaving from the hot surface reaches it global maximum. The speed of the wetting front indicates the quench ability of the hot surface for the corresponding flow conditions and the coolant. Wetting front tracking is more important for the prediction of surface temperature during quenching. This research works presents the combined numerical and experimental aspects of the heat flux estimation during the quenching process. At any instant, the position of the wetting front is simply assumed as the location of maximum heat flux. This assumption implicitly treats the wetting front as a line instead of area. The location of wetting front and its velocity at every instant are determined by using the experimental temperature data and the inverse algorithm. Experimental setup and temperature measurement technique are explained in detail. The developed inverse algorithm predicts the quenched side temperature and heat flux from the measured side temperature. A two-dimensional Inverse Heat Conduction Problem (IHCP) is solved through the non iterative Finite Element Method (FEM). The considered quenching technique for the study, based on the method of coolant supplied which is array of water jets. One kind of coolant used in this study is tap water. Aluminum 2024, Inconel, and Nickel are the three different materials considered for the analysis. A rectangular plate made of Nickel with dimension 140 × 70 × 2 mm, using the same dimensions of the Inconel. As in the case of the use of Aluminum, the thickness is the only change to 3 mm, the plate quenched by array of water jets with velocities 0.9 m/s, 1.2 m/s, 1.5 m/s and 1.8 m/s. The measured temperature data are further processed through the inverse finite element technique for the estimation of heat flux leaving from the quenched surface. The position of maximum heat flux changes with time which indicates the movement of wetting front. In this work, four different coolant velocities are employed, and the change in coolant velocity strongly affects the heat flux and wetting front movement.

scholarly journals ELETRIC FIELD ENHANCEMENT AND DETERIORATION OF BOILING HEAT TRANSFER AND CRITICAL HEAT FLUX IN DIELECTRIC FLUIDS

2002 ◽  
Vol 1 (1) ◽  
Author(s):  
P. M. Carrica ◽  
V. Masson
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Electric Fields ◽  
Boiling Heat Transfer ◽  
Nucleate Boiling ◽  
Film Boiling ◽  
Two Phase ◽  
Boiling Regime ◽  
Dielectric Fluids

We present the results of an experimental study of the effects of externally imposed electric fields on boiling heat transfer and critical heat flux (CHF) in dielectric fluids. The study comprises the analysis of geometries that, under the effects of electric fields, cause the bubbles either to be pushed toward the heater or away from it. A local phase detection probe was used to measure the void fraction and the interfacial impact rate near the heater. It was found that the critical heat flux can be either augmented or reduced with the application of an electric field, depending on the direction of . In addition, the heat transfer can be slightly enhanced or degraded depending on the heat flux. The study of the two-phase flow in nucleate boiling, only for the case of favorable dielectrophoretic forces, reveals that the application of an electric field reduces the bubble detection time and increases the detachment frequency. It also shows that the two-phase flow characteristics of the second film boiling regime resemble more a nucleate boiling regime than a film boiling regime.

Modeling Cladding-Coolant Heat Transfer of High-Burnup Fuel During RIA

2006 ◽  
Author(s):  
Wenfeng Liu ◽  
Mujid S. Kazimi
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Thermal Properties ◽  
Heat Conduction ◽  
Nucleate Boiling ◽  
Boiling Temperature ◽  
Film Boiling ◽  
Solid Contact ◽  
Boiling Regime ◽  
High Burnup

This paper describes a model for the cladding-coolant heat transfer of high burnup fuel during a Reactivity Initiated Accident (RIA) which is implemented in the fuel performance code FRAPTRAN 1.2. The minimum stable film boiling temperature, affected by the subcooling and the clad oxidation, is modeled by a modified Henry correlation. This accounts for the effects of thermal properties of the cladding surface on the transient temperature drop during liquid-solid contact. The transition boiling regime is described as the interpolation of the heat flux between two anchor points on the boiling curve: the Critical Heat Flux (CHF) and minimum stable film boiling. The CHF correlation is based on the Zuber hydrodynamic model multiplied by a subcooling factor. Frederking correlation is chosen to model the film boiling regime. The heat conduction through the oxide layer of the cladding surface of high burnup fuel is calculated by solving heat conduction equations with thermal properties of zirconia taken from MATPRO. This model is validated in the FRAPTRAN code for test cases of both high burnup and fresh test fuel rods including the burnup level (0–56 MW d/kg), peak fuel enthalpy deposit (70–190 cal/g), degree of subcooling (0–80 °C), and extent of oxidation (0–25 micron). The modified code demonstrates the capability of differentiating between the departure from nucleate boiling (DNB) and none-DNB cases. The predicted peak cladding temperature (PCT) and duration of DNB achieves generally good agreement with the experimental data. It is found that the cladding surface oxidation of high burnup fuel causes an early rewetting of cladding or suppresses DNB due to two factors: 1) Thick zirconia layer may delay the heat conducted to the surface while keeping the surface heat transfer in the most effective nucleate boiling regime. 2) The transient liquid-solid contact resulting from vapor breaking down would cause a lower interface temperature for an oxidized surface, essentially raises the minimum stable film boiling temperature.

Boiling Heat Transfer Characteristics of Rotary Hollow Cylinders with In-Line and Staggered Multiple Arrays of Water Jets

2021 ◽  
Author(s):  
Mohammad Jahedi ◽  
Bahram Moshfegh
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Stagnation Point ◽  
Surface Heat Flux ◽  
Surface Heat ◽  
Maximum Heat ◽  
Water Jets ◽  
Maximum Heat Flux ◽  
Inner Surface ◽  
Hollow Cylinders

Abstract Transient heat transfer studies of quenching rotary hollow cylinders with in-line and staggered multiple arrays of jets have been carried out experimentally. The study involves three hollow cylinders (Do/d = 12 to 24) with rotation speed 10 to 50 rpm, quenched by subcooled water jets (ΔTsub=50-80 K) with jet flow rate 2.7 to 10.9 L/min. The increase in area-averaged and maximum heat flux over quenching surface (Af) has been observed in the studied multiple arrays with constant Qtotal compared to previous studies. Investigation of radial temperature distribution at stagnation point of jet reveals that the footprint of configuration of 4-row array is highlighted in radial distances near the outer surface and vanishes further down toward the inner surface. The influence of the main quenching parameters on local average surface heat flux at stagnation point is addressed in all the boiling regimes where the result indicates jet flow rate provides strongest effect in all the boiling regimes. Effectiveness of magnitude of maximum heat flux in the boiling curve for the studied parameters is reported. The result of spatial and temporal heat flux by radial conduction in the solid presents projection depth of cyclic variation of surface heat flux in the radial axis as it disappears near inner surface of hollow cylinder. In addition, correlations are proposed for area-averaged Nusselt number as well as average and maximum local heat flux at stagnation point of jet for the in-line and staggered multiple arrays.

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